This is the backstory to how and why the periodic table is arrange the way it is.

We all remember our science classes, and memorizing the first 20 elements on the periodic table. Oh boy o boy! We all hated it. Period! Hmmm? So who on Earth even came up with such a weird arrangement of the fact that the oxygen you breathe in is heavier than the carbon essential for life. Duh? This isn’t the genius work of one individual, but several scientists over the course of decades leading to a century of collaboration. Dear friends, let us tell you the history behind why you had to recite the mnemonics of the periodic table.



Once Upon All Elements

The periodic table is commonly seen in science textbooks, classrooms, and laboratories. This is one of the most popular exhibits in science besides the figure of the atom. It is not just a mere tabular arrangement of the elements for easy identification. It is used in various ways by scientists to analyze reactivity among elements, predict chemical reactions, understand certain trends in the periodic properties of elements, and even speculate where on the table a new element will be placed. Sounds like a fortune telling table for scientists.

It is called the periodic table because of the horizontal and vertical arrangement of the elements. You’ve notice that there are rows and columns, the horizontal rows (from left to right) are known as periods, whereas the vertical columns (from top to bottom) are known as groups. However, the table as you know is arranged into their atomic numbers and periodic properties. Throughout history, several scientists worked for nearly a century to assemble the table this way.

Notable of these renowned scientists include, Antoine Lavoisier, Johann Wolfgang Döbereiner, John Newlands, Henry Moseley, Lothar Meyer, and the father of the periodic table himself, Dmitri Mendeleev — the man who arranged it the way it is today (more on him later).

In 1789, French chemist Lavoisier tried to group the elements into metals and non-metals but that wasn’t it. Forty years on, German physicist Döbereiner noticed some similarities in the physical and chemical properties of certain elements. He then arranged them into three groups in increasing order of their atomic mass known as triads. But he also noticed that some properties of the middle elements — such as those with atomic mass and density — were approximately the value of these properties of the other two in each triad.

Unfortunately this isn’t the table you know, so in 1860, a new publication of the table was revised with the atomic masses of the elements, at the first International Conference of Chemistry in Karlsruhe, Germany. This was the first time hydrogen was made first on the table because it had an atomic mass of one, and the others were decided by comparing them with it. For instance, if carbon (C) was 12 times heavier than hydrogen (H), it had an atomic mass of 12.



Oh! Men Delving Deep

The elements were first arranged into a periodic table with the increasing order of their atomic masses by British chemist Newlands. He found similarities between every eighth element on the table and called this trend the law of octaves — grouping them into groups of eight (but left no spaces for undiscovered elements). However, in 1869, it was Russian chemist Mendeleev who laid down the foundation for the modern periodic table — even leaving spaces for yet to be discovered elements.

Mendeleev found that some elements didn’t fit into certain groups of the table. He would either rearrange them or leave those spaces for future elements. He was even able to predict some elements that were not yet discovered. For instance, he labelled a space “eka-aluminium” for an undiscovered element that had similar properties to (you guessed it) aluminium (Al). This was later discovered as gallium (Ga), however, there were a few discrepancies, such as the positions of iodine (I) and tellurium (Te), which were not fully understood.

In 1870, German chemist Meyer came up with a version of the periodic table similar to Mendeleev’s. He also left spaces for undiscovered elements but did not predict their properties.  In 1882, the Royal Society of London awarded Mendeleev and Meyer with the Davy Medal — the highest award in the field of chemistry. The elements predicted by Mendeleev were later discovered which proved that his predictions were accurate. In 1955, the 101st element was named mendelevium (Md) in honor of his achievement.



Whence Cometh Thy Periods?

Aforementioned, the periodic table is arranged into rows (with metals on the extreme left, and non-metals on the right), and columns (which consists of elements with similar chemical properties). In 1913, English physicist Moseley applied X-rays to determine the wavelengths of elements and made a correlation with their atomic numbers. And later arranged the elements on the periodic table based on atomic numbers. This finally explained the earlier disparities that had applied their atomic masses.

The periodic table provides information about the atomic structure of the elements and chemical similarities or dissimilarities between them. It is used in developing chemicals for every day used — from pharmaceuticals to cosmetics to petrochemicals to the electronics used in devices. The 2019 marked the 150th anniversary of Mendeleev’s first publication. And that particular year was named the International Year of the Periodic Table by the United Nations Educational, Scientific, and Cultural Organization (UNESCO).

The Periodic Table of Chemical Elements is more than just a guide or catalogue of the entire known atoms in the universe;” UNESCO wrote on its official website. “it is essentially a window on the universe, helping to expand our understanding of the world around us.”


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Written by: Nana Kwadwo, Wed, Oct 06, 2021.

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